It is known to apply AC plasma excitation fields to a region of a vacuum chamber for plasma processing a workpiece, wherein the region is coupled to a gas that the fields convert into the processing plasma. The workpiece is usually a semiconductor wafer, or dielectric plate and the plasma is involved in forming integrated circuit features on the workpiece. The excited plasma typically dry etches the workpiece, but in some instances results in materials being deposited on the workpiece. Typically, the AC plasma excitation fields are supplied to the region by a pair of spaced electrodes in the chamber or one electrode in the chamber and a coil, located outside the chamber. (It is to be understood that the term “reactance” when used in the present document in connection with a vacuum plasma processing chamber refers to an electrode or a coil for supplying AC plasma excitation fields to a plasma in the chamber.)
As the size of the features continues to decrease, there are increased requirements for precise control of various parameters of the plasma processing a workpiece. These parameters include characteristics of the AC fields that the reactance couples to the plasma. In particular, the intensity and shape of the AC fields that the reactance couples to the plasma have a substantial effect on the nature of the workpiece features.